The present invention relates to a tubular corrugated bellows element for fluids, that is to say liquids or gases, with a plurality of corrugations running concentrically round the bellows axis in successive fashion. Annular spaces are provided between the flanks of adjacent bellows corrugations; these spaces become narrower at the inner ends of the corrugations, which are of flat form.
Corrugated bellows elements comprise an elastic structure in which generally undesired vibrations may readily be caused when liquid or gaseous material flows through the element. The cause of such vibration or oscillation is, generally speaking, the formation of eddies within the annular spaced between the corrugations. Such fluid-caused vibration may have mixed with, or been superimposed on, external mechanical vibrations acting on the bellows element by way of the structures joined therewith. This form of vibration is specially important when such bellows elements are used as compensators in exhaust systems, more specially in motor vehicles in fact, for such purposes, normal corrugated-pipe bellows element compensators may not be generally used.
When used in this fashion it is necessary, for this reason, to make use of a guide pipe within the bellows element, and to shut off the ring-spaces between the bellows corrugations from the inside of the bellows so that the forming of eddies or vortices is completely out of the question. In addition to the increased price of producing and fixing such bellows elements when in position, such elements may be used when only acted upon only by axial forces, because changing their angles is not possible without damage, and because sideways motion is only possible within certain tight limits.
Although motion will be freer if a flexible pipe is used in place of the stiff guide pipe (see German Pat. No. 816,465), troublesome conditions are more likely, to arise, particularly when axial motion is desired, because the elasticity of the flexible pipe in the axial direction, particularly when under pressure, is very much less than the resilient capacity of the compensator. For this reason, if axial motion takes place past a certain limit, the flexible pipe will kink for this reason, dependent on the wall thickness, the compensator may also be kinked. Furthermore, such a flexible pipe may only be used with certain sorts of fluids.
To permit the last-named sort of motion occur, at least to a limited degree, a further suggestion has been made in the prior art (see German specification No. 2,651,661) for placing a wire fabric, made into the form of a pipe, within the bellows element. Such an element is, however, naturally high in price which respect to its production and placement.
In the case of a simpler design, of the sort noted earlier in this specification (see U.S. Pat. No. 2,876,801), a smooth inner wall within a corrugated pipe is to be produced, for getting better flow conditions for fluids, by so designing the flanks of the bellows corrugations, and by making the ring-space between them narrower while running inwardly in parallel fashion to the axis of the corrugated pipe. The bellows' inner corrugation ends are made flat so that in the direction of flow, a generally pipe-like wall structure is produced. With this known bellows structure, it may be that undesired flow conditions are eliminated; this occurs, however, only in the case of static conditions. For example, axial motion of the corrugated bellows element is very limited so that, if anything, only stretching forces, but not compression forces, may be taken up by the bellows element, because, in the case of compression forces, the inner corrugation ends of the bellows element are pushed together, even by a very small motion, and they will necessarily be bent. Furthermore, changes in angle (between the two ends of the bellows) are generally not possible, because, in this case, the inner corrugation ends of the bellows element on the envelope line up with the smaller radius of curvature, and they will necessarily be pushed up against each other. For correcting such undesired flow conditions, it is necessary, in the case of such a bellows element, to make a design such that there is no axial motion and change in angle or bending, such motion, however, being the main function of a corrugated bellows element.